Frontier Airlines Holdings Inc. is asking for bankruptcy court permission to sell off four airplanes for $106 million, noting in court papers that the company’s budget for the coming months relies on the infusion of cash the sale would generate, Bankruptcy Law360 reported yesterday. Denver-based Frontier filed a motion on Friday seeking authorization to enter into a letter of intent and to sell two Airbus A319-111 aircraft and two Airbus A318-111 aircraft to Verulamium Finance Ltd. Verulamium would pay $106 million for the four planes, $68.5 million of which would go to pay for the mortgages on each of the aircraft, leaving Frontier with $37.5 million.